Benchmark: querySelector vs getElementsByTagName[0] iteration

HTML Preparation code:

<div></div>
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Tests:

querySelector
const target = document.querySelector('div'); if(target) { console.log(target); } else { console.log('daddy'); }
getElementsByTagName[0]
const target = document.getElementsByTagName('div')[0]; if(target) { console.log(target); } else { console.log('daddy'); }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
querySelector
getElementsByTagName[0]

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.64 Safari/537.36 Edg/101.0.1210.53

Browser/OS: Chrome 101 on Windows

View result in a separate tab

Test name	Executions per second
querySelector	129328.6 Ops/sec
getElementsByTagName[0]	18001.1 Ops/sec

Autogenerated LLM Summary (model llama3.2:3b, generated 2 months ago):

LLMs can make mistakes. Check important info.

**Overview of the Benchmark**

The provided benchmark is designed to measure the performance difference between two methods for selecting HTML elements: `document.querySelector` and `document.getElementsByTagName`. The test cases are run on multiple browsers and devices, allowing users to compare results across different platforms.

**Test Case Descriptions**

There are two individual test cases:

1. **querySelector**: This test case uses the `document.querySelector` method to select an element with the tag name "div". It then checks if the selected element exists (i.e., is not null or undefined) and logs it to the console if true.
2. **getElementsByTagName[0]**: This test case uses the `document.getElementsByTagName` method to get a list of all elements with the tag name "div" and then selects the first element from the list using `[0]`. It then checks if the selected element exists (i.e., is not null or undefined) and logs it to the console if true.

**Comparison of Options**

The two methods are compared in terms of performance:

* **querySelector**: This method is generally faster because it returns only the first matching element, whereas `getElementsByTagName` returns all elements that match the specified tag name. This can lead to better performance for small datasets or when working with complex selectors.
* **getElementsByTagName[0]**: However, this method requires more memory and processing power because it needs to iterate over the entire list of elements before selecting the first one.

**Pros and Cons**

* **querySelector**: Pros:
	+ Faster execution time
	+ Returns only the first matching element, which can improve performance for small datasets or complex selectors
* Cons:
	+ May not work correctly for certain use cases (e.g., when there are multiple elements with the same selector)
* **getElementsByTagName[0]**: Pros:
	+ Works correctly in all cases (i.e., returns all matching elements and allows selection of any element from the list)
* Cons:
	+ Slower execution time due to memory and processing overhead

**Library/Functionality Used**

The `document.querySelector` method is a part of the DOM API, which provides an interface for working with HTML documents.

**Special JS Feature/Syntax**

There are no special JavaScript features or syntax used in this benchmark. It only relies on standard JavaScript methods and DOM API functions.

**Alternatives**

If you're looking for alternatives to these methods, consider the following:

* **CSSOM Query**: Instead of using `document.querySelector`, you can use the CSSOM query API to select elements based on their styles or other properties.
* **XPath Expression**: You can also use XPath expressions to select elements from an XML document. This method is more complex and not directly applicable to HTML documents, but it provides a powerful way to navigate and manipulate element hierarchies.

In summary, the benchmark highlights the performance difference between two common methods for selecting HTML elements: `document.querySelector` and `document.getElementsByTagName`. The results can help users choose the most efficient approach depending on their specific use case and requirements.

Related benchmarks:

querySelector vs getElementsByTagName[0] iteration (version: 0)

Comparing performance of: querySelector vs getElementsByTagName[0]

Created: 2 years ago by: Guest

Jump to the latest result

querySelector

getElementsByTagName[0]

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

Autogenerated LLM Summary (model llama3.2:3b, generated 2 months ago):